Activist investor Bill Ackman (above) is throwing his financial weight around in his high-stakes bout with Herbalife, which he accuses of being a pyramid scheme. Photo: Reuters

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The first two rounds of Bill Ackman’s latest Wall Street fight have been a walkover.

Locked in a battle with Herbalife, the 32-year-old nutritional supplement maker he has ripped over the past 48 hours as a pyramid scheme, Ackman has sparked a two-day, sell-off of the company’s shares of 20.7 percent.

Herbalife, based in the Cayman Islands, closed yesterday at $33.70, off 9.7 percent to a 52-week low after Ackman’s comments at a Manhattan financial conference.

A day earlier, in a TV interview, he announced he had shorted the shares of the $3.5 billion global brand — causing a 10.9 percent drop in its shares.

“This is the highest conviction I’ve ever had about any investment I’ve ever made,” Ackman said yesterday in a series of interviews.

The investor told CNBC that he expects the Federal Trade Commission will take a “hard look” at the company.

The heavyweight battle picked up steam over the last two days and has become, in the typically slow days leading up to Christmas, one of the most-watched events on Wall Street.

As the financial world watched, Herbalife CEO Michael Johnson returned fire — calling Ackman’s statements “bogus” and asking the Securities and Exchange Commission to probe the motives of Ackman and his Pershing Square Capital hedge fund.

A spokeswoman said if Johnson were allowed the chance to face-off against the investor at the Downtown conference, the CEO “would have been able to tear Mr. Ackman’s premises and interpretation of our business model apart.”

Ackman’s misstatements and mistakes are too numerous to address immediately, the spokeswoman snapped.

Ackman is renowned for enlisting the media to promote Pershing’s investments — and he is doing it up big with Herbalife.

In the series of TV interviews, Ackman laid out a detailed case against Johnson’s multi-level marketing company, saying that to increase profits it must continue to expand its sales territory and enlist new independent distributors, who often end up owning product that they cannot sell.

The company has recently expanded to such African countries as Ghana — a location that Ackman found especially intriguing.

“The problem is they are running out of countries,” said Ackman, who said he would donate any Herbalife profits to charity.

The twitterati quickly assessed the move as brilliant marketing.

“Ackman is essentially shorting $HLF just to get a reputation. And for charity. Beyond gangsta,” tweeted “Downtown” Josh Brown, who uses the Twitter handle “@reformed broker.”

Ackman’s Herbalife dust-up comes ahead of a move to take his Pershing Square Holdings public next year in London.

Lately, Ackman’s performance is lagging the market — largely due to Pershing’s stake in JCPenney, which is down 42 percent this year.

Pershing Square was up around 6 percent through September, according to a November investor letter.